The term ‘plain’ traverses the depth-psychology corpus along two largely independent axes, each with its own symbolic freight. In the mythological and epic registers — Homer, Plato’s Critias, and Campbell’s comparative mythology — the plain functions as a liminal topographic zone: the arena of combat, the site of cosmic conflagration, the cultivated and measured space that stands in productive tension with mountain, sea, and underworld. Hephaestus sets ‘the plain alight’ in the Iliad; Plato’s Atlantean plain is a geometrically ordered, humanly labored landscape that mirrors the ordered psyche of an ideal civilization; Campbell’s ‘plain of heaven’ is the cosmic stage on which divine concealment and revelation are enacted. In a secondary, methodological register — surfacing in Lattimore’s translatorial manifesto and Thompson’s critique of Dawkins — ‘plain’ operates as an epistemological claim: to be ‘plain and direct in thought and expression’ (Arnold’s criterion for Homer, cited by Lattimore) is an aesthetic and ethical demand, while Thompson’s ironic deployment of ‘the plain truth’ to refute genetic literalism exposes how claims to plainness can mask metaphysical assumptions. The concordance entry thus maps a field in which spatial, symbolic, and epistemological senses of the term intersect, making ‘plain’ a surprisingly revealing index of how these traditions negotiate clarity, order, and elemental power.